Hi all,
I'm building a SE KT88 amplifier.
At the moment I'm building the PSU, a 300+300 mosfet regulated HT PS.
The amplifier will be a parafeed, with a KT88 on top as a CCS (driven by a SS CCS).
THIS is the amplifier output stage; I have already tried the CCS with the KT88 pentode (on B+ 300V) and it seems to work fine.
The B+, as said, will be 600V.
Now, while preparring the PSU, I have to decide on the driver.
I have some 12AX7, ECL84, and can easily trade them with some 6SN7 or 6SL7.
I have also to decide the driver topology: SE, SE + CCS on top (the same of the output stage), SRPP, mu-follower?
My preferred solution is to use the ECL84 (or EL84) pentode stage, strapped as triode, in a SE configuration, maybe loaded with a CCS (a EL84 pentode driven by a SS CCS).
What do you think? which driver would you use for such a amplifier?
Ciao,
Giovanni
I'm building a SE KT88 amplifier.
At the moment I'm building the PSU, a 300+300 mosfet regulated HT PS.
The amplifier will be a parafeed, with a KT88 on top as a CCS (driven by a SS CCS).
THIS is the amplifier output stage; I have already tried the CCS with the KT88 pentode (on B+ 300V) and it seems to work fine.
The B+, as said, will be 600V.
Now, while preparring the PSU, I have to decide on the driver.
I have some 12AX7, ECL84, and can easily trade them with some 6SN7 or 6SL7.
I have also to decide the driver topology: SE, SE + CCS on top (the same of the output stage), SRPP, mu-follower?
My preferred solution is to use the ECL84 (or EL84) pentode stage, strapped as triode, in a SE configuration, maybe loaded with a CCS (a EL84 pentode driven by a SS CCS).
What do you think? which driver would you use for such a amplifier?
Ciao,
Giovanni
Cant advise on what would be best, but loading the driver with a CCS will maximise your voltage gain and linearity. The LED biased two transistor CCS which SY developed works a treat.
Where did you get the design for your KT88 CCS, and how does it perform. I am currently converting my RH807 parafeed amp from CCS loaded to use chokes loaded - just need the chokes now !
Shoog
Where did you get the design for your KT88 CCS, and how does it perform. I am currently converting my RH807 parafeed amp from CCS loaded to use chokes loaded - just need the chokes now !
Shoog
Giovanni,
As you seem to be happy with hybrid Solid State plus Tube circuits and designing around MOSFETS then I recommend that you look at the PowerDrive circuits on Tubelab's website.
http://www.tubelab.com/
The PowerDrive is a CCS loaded triode stage followed by a MOSFET Source follower to drive the output tube grid.
Its a nice fit with your existing circuits and is certainly high end in terms of performance.
Cheers,
Ian
As you seem to be happy with hybrid Solid State plus Tube circuits and designing around MOSFETS then I recommend that you look at the PowerDrive circuits on Tubelab's website.
http://www.tubelab.com/
The PowerDrive is a CCS loaded triode stage followed by a MOSFET Source follower to drive the output tube grid.
Its a nice fit with your existing circuits and is certainly high end in terms of performance.
Cheers,
Ian
Shoog:
The idea to drive (bias) a pentode with a solid state CCS comes from Kuei Yang Wang, we had a long thread about CCS here.
The schematic, instead, is mine.
I'm trying now a different version, with the use of a OP amp, in manner to have a feedback and improve the CCS dynamic and impedance.
Gingertube:
I know the smart PowerDrive idea, George (TubeLab) made a wonderful job on it.
I already tried a home made dual PowerDrive (to balance the bias of two paralleded KT88) in a SE amp prototype, and it worked not too bad (it was a new design, and it needed lot of work to be fully functional); due to lack of time I never finished it.
Moreover, it was too complex for me.
This is the circuit.
I would like to keep the "sand" to a minimum: I mean, use the SS stuffs only where they are really necessary.
This means, in my current vision, using SS circuit only for a CCS, and try to use tube for everything else (also for the driver).
The CCS would be used only to improve the linearity, as you said, instead to use a resistor.
My idea is to go with the ECL84 pentode section, CCS loaded.
The triode section of the same tube will be used, instead, to create an active low-pass filter in manner to drive an external subwoofer amplifier.
Ciao,
Giovanni
The idea to drive (bias) a pentode with a solid state CCS comes from Kuei Yang Wang, we had a long thread about CCS here.
The schematic, instead, is mine.
I'm trying now a different version, with the use of a OP amp, in manner to have a feedback and improve the CCS dynamic and impedance.
Gingertube:
I know the smart PowerDrive idea, George (TubeLab) made a wonderful job on it.
I already tried a home made dual PowerDrive (to balance the bias of two paralleded KT88) in a SE amp prototype, and it worked not too bad (it was a new design, and it needed lot of work to be fully functional); due to lack of time I never finished it.
Moreover, it was too complex for me.
This is the circuit.
I would like to keep the "sand" to a minimum: I mean, use the SS stuffs only where they are really necessary.
This means, in my current vision, using SS circuit only for a CCS, and try to use tube for everything else (also for the driver).
The CCS would be used only to improve the linearity, as you said, instead to use a resistor.
My idea is to go with the ECL84 pentode section, CCS loaded.
The triode section of the same tube will be used, instead, to create an active low-pass filter in manner to drive an external subwoofer amplifier.
Ciao,
Giovanni
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